Various types of packages are formed from flexible film structures and prepared with a form-fill-seal process. Such processes comprise different steps allowing to prepare leak-free formed packages in a cost effective manner. A traditional process could be described in three successive steps, in which the package is firstly formed from the film structure, after which it is filled and finally sealed or closed. Past improvements were mostly concerned with increasing the speed of the existing processes.
A way to optimise sealing or closing speed is known from WO9500587 published on the Jan. 5, 1995. The improvement is not achieved through a modification of the process but through a modification of the sealing materials, when metallocene catalysed polyolefins are used as a sealant layer. The advantage of this type of material is its low melting temperature. In case of heat sealing methods, there is a temperature range above which the seal would be burnt and below which the seal would not be sufficiently strong. For this reason, use of metallocene catalysed polyolefins as a sealant layer allows an enlargement of the sealing range because the bottom limit of the range, called the hot tack seal initiation temperature, is brought down as metallocene catalysed polyolefins melt at lower temperature when compared to traditional polyolefins. For example, the line speed of known packaging equipment used for manufacturing sachets such as form, fill and seal machines, is limited by the sealing properties of the traditional polyolefin films used in the machines. Traditional films have high hot tack seal initiation temperatures and a narrow sealing range. Therefore, the rate at which a form, fill and seal machine can produce sachets is limited. If the heat seal temperature range where one could obtain strong seals is broadened, then the speed of a form, fill and seal machine can be increased and, thus, the rate at which sachets can be produced can be increased. This improvement introduced by WO9500587 is quantitative as it allows an increased processing speed to be applied to known processes, such as those described in U.S. Pat. No. 4,521,437.
The present invention relates to a process for producing a four sided seal sachet filled with a volume of flowable material, the process comprising at least three steps, the first step consisting of forming the sachet, the second step consisting of filling the formed sachet with the volume of flowable material and the third step consisting of closing the filled sachet, the sachet being made of a flexible film, the flexible film comprising a metallocene catalysed resin, the formed sachet having a rectangular shape with a length L (11) and a width W (12) in between seals.
The present invention also encompasses a sachet filled with a volume of flowable material, the sachet being made of a flexible film, the flexible film comprising a metallocene catalysed resin, the sachet being a four sided seal sachet (10) having two longitudinal seals (70) and two transversal seals, each of the longitudinal seals (70) intersecting both of the transversal seals at substantially right angle, the longitudinal segment comprised between the intersections having a length L, the transverse segment comprised between the intersections having a length W.
This improvement is applied to a well known sealing process described in U.S. Pat. No. 4,521,437, patented on the Jun. 4, 1985, which can be made on a so-called vertical form and fill machine. Using such a machine, a flat web of synthetic thermoplastic film is unwound from a roll and formed into a continuous tube in a tube forming section, by sealing the longitudinal edges on the film together to form a so-called lap seal or a so-called fin seal (70). The tube thus formed is pulled vertically downwards to a filling station. The tube is then collapsed across a transverse cross-section of the tube, the position of such cross-section being at a sealing device below the filling station. A transverse heat seal is made (71), by the sealing device, at the collapsed portion of the tube, thus making an air tight seal across the tube. The sealing device generally comprises a pair of jaws. After making the transverse seal (71), a pre-set volume of material to be packaged, e.g. flowable material (80), is allowed to enter the tube, at the filling station, and fill the tube upwardly from the aforementioned transverse seal (71). The tube is then allowed to drop a predetermined distance under the influence of the weight of the material in the tube and of the film advance mechanism on the machine. The jaws of the sealing device are closed again, thus collapsing the tube at a second transverse section, which is above the air/material interface in the tube. The sealing device seals and severs the tube transversely at said second transverse section (90). The material-filled portion of the tube is now in the form of a pillow shaped sachet. Thus the sealing device has sealed the top of the filled sachet (91), sealed the bottom of the next-to-be-formed sachet (92) and separated the filled sachet from the next-to-be-formed sachet, all in one operation.
The existing processes described in U.S. Pat. No. 4,521,437 aims to avoid what is called contamination of the sealing regions. Contamination occurs when the contained material enters the sealing region to seal prior or/and during the sealing operation. Contamination becomes particularly frequent as the package size reduces, because the level of the contained product is closer to the sealing region. Therefore, there is a chance that product can enter the seal region due to splashing or foaming (for liquid products), or because of bouncing and shaking (for powder products). In some cases, particularly concerning liquids or powders containing a high level of surfactants, this can lead to poor seal quality and to product leakage. For powder, the fine granules within the powder can prevent the flow of the sealing material in the seal region from contacting the seal surfaces. For the liquid, especially if viscous or if containing surfactants, the liquid can be difficult to squeeze out during the seal process because it can wet the region within the seal. Both these examples can result in lower seal strength or, in extreme situations, no seal at all.
Consequently, the contamination has to be prevented. In order to prevent contamination, the pre-set volume of material to be packaged is reduced so that the air/material interface is brought down to a level at which contamination does not occur, after what sealing is made above the air/material interface as described in U.S. Pat. No. 4,521,437. Sealing can then be made in a faster and more reliable manner as the seal region is not contaminated. The disadvantage is that the volume availabe in the package is not used to maximum capacity, so that part of the package material is wasted.
The present invention is aiming at increasing the pre-set volume of flowable material contained in a four sided seal sachet by sealing through partial or complete contamination instead of avoiding contamination. The aim is to render it possible to seal through flowable materials, so that the packing process can be redesigned in a more efficient manner.